A MEMS device using micro-electromechanical systems (MEMS), for example, a radio-frequency (RF) circuit using a MEMS variable capacitance element, is expected to be used in next generation radio systems because of the reduced output signal loss of the MEMS variable capacitance element and excellent output signal linearity (JP 2008-278634).
A MEMS variable capacitance element is produced in a backend process, and is formed in an interconnect level higher than a semiconductor integrated circuit formed on a semiconductor substrate. Passive elements such as an inductor and a capacitance element having a metal-insulator-metal (MIM) structure are formed simultaneously in the same interconnect level as is a MEMS variable capacitance element.
A MIM capacitance element is formed to have a large capacitance corresponding to required characteristics. Therefore, a MIM capacitance element is required to incorporate an insulator having a high dielectric constant, and/or an insulator having a small thickness in the insulator interposed between opposing electrodes (metals).
In contrast, a MEMS variable capacitance element is influenced by the surface roughness of a component electrode or insulator, and the influence of the thickness and dielectric constant of the insulator on the capacitance is not as large in a MEMS variable capacitance element as in a MIM capacitance element. However, considering the reliability of an insulator constituting a MEMS variable capacitance element, the thickness of an insulator used in a MEMS variable capacitance element is desirably as thick as possible in a range of realizing a desired capacitance, in order to reduce an electric field produced between opposing electrodes.
As described above, different characteristics are required for an insulator constituting a MEMS variable capacitance element, and an insulator constituting a MIM capacitance element.
However, as described above, a MEMS variable capacitance element and MIM capacitance element are formed simultaneously in the same manufacturing process, and it is difficult to construct the insulators constituting the these elements given the required characteristics.